1. Field of the Invention
The present invention relates to communication equipment and, more specifically, to plasmonic circuits.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art and/or what is not in the prior art.
Surface plasmons (SPs), also often referred to as surface-plasmon polaritons, are surface-bound waves that can propagate, e.g., along a metal-dielectric interface or along a metal-vacuum interface. SPs can be qualitatively viewed as a combination of electromagnetic waves and associated charge waves. The electromagnetic waves propagate along the interface due to their interaction with free surface charges of the metal. The interaction also causes the surface charges to oscillate in resonance with the electromagnetic wave. The combined physical entity created via this resonant interaction, i.e., an entity including a charge wave and an electromagnetic wave, is an SP. A detailed description of certain physical properties of SPs can be found, e.g., in an article by W. L. Barnes, et al., entitled “Surface Plasmon Subwavelength Optics,” published in Nature, 14 Aug. 2003, v. 424, pp. 824-830, the teachings of which are incorporated herein by reference in its entirety.
One problem with SPs is that their propagation is typically characterized by a relatively high rate of attenuation and/or dissipation. More specifically, a beam of SPs propagating along a metal-dielectric interface is attenuated, primarily due to resistive losses in the metal. The rate of attenuation depends on the wavelength and the complex dielectric function of the metal. For example, in the visible spectrum, SP propagation distances along a silver-dielectric interface are in the range between about 10 μm and about 100 μm. Jette-Charbonneau et al. (see Optics Express, 2005, v. 13, p. 4674) describe structures/materials, in which SP propagation distances are in the sub-millimeter range.